1. Field of the Invention
The present invention relates to a controller for a homogeneous charge compression ignition internal combustion engine which compresses a fuel-air mixture of a fuel and air to make a spontaneous ignition.
2. Description of the Related Art
In recent years, a homogeneous charge compression ignition internal combustion engine (so-called HCCI engine) has drawn attention as an engine with high efficiency and less discharge such as nitroxide or the like. The homogeneous charge compression ignition internal combustion engine (hereinafter, referred to as the HCCI engine where appropriate) compresses a fuel-air mixture of a fuel and air to a high temperature in a combustion chamber of a cylinder to make the fuel-air mixture spontaneously ignited to combustion.
In this type of HCCI engine, proceeding of a chemical reaction (oxidation reaction) on the fuel-air mixture varies according to various contributing factors such as a temperature condition in the cylinder, an air-fuel ratio of the fuel-air mixture, an octane number of a fuel and the like. Thereby, it has become an important task how to control a combustion timing (ignition timing) of the fuel-air mixture at an appropriate timing.
Thus, as a control technology of this type of HCCI engine, there has been known one disclosed, for example, in Japanese Patent Laid-open No. 2006-226172 (hereinafter, referred to as Patent Document 1), or in Japanese Patent Laid-open No. 2000-179368 (hereinafter, referred to as Patent Document 2). According to the control technology disclosed in Patent Document 1 or 2, it is possible to supply two types of fuels having mutually different octane numbers (ignitability) to a cylinder of an engine independently, and a supplied proportion of the respective fuel is adjusted according to a load of the engine. Thereby, the ignition and combustion of the fuel-air mixture are stabilized in a wide working area varying from a low-load area to a high-load area.
Meanwhile, it is considered that in addition to decrease as much as possible fuel consumption of the HCCI engine, it is preferable to include as a working mode of the HCCI engine a fuel-cut mode which forcibly switches off the supply of a fuel to the HCCI engine at a predefined condition such as deceleration or the like of a vehicle with the engine mounted thereon.
However, since the combustion of the fuel-air mixture is not performed in the combustion chamber of the HCCI engine in the fuel-cut mode, the inner temperature of the combustion chamber or the temperature of the wall surface of the cylinder decreases. As a result, the inner temperature of the combustion chamber or the temperature of the wall surface of the cylinder becomes low at a time immediately after the working mode returned from the fuel-cut mode to a normal mode in which the combustion of the fuel-air mixture is performed in the combustion chamber. Thus in such case, even though a supplied quantity of each fuel to the combustion chamber is controlled in a same way as that in a continuous working in the normal mode, it is difficult to make the fuel-air mixture ignited in the HCCI engine and it is easy for the ignited fuel-air mixture to get extinguished.
Therefore, there is desired a method for igniting efficiently the fuel-air mixture immediately after the working mode is returned from the fuel-cut mode to the normal mode.
However, the above-mentioned method is not applied by the conventional HCCI engine as disclosed in either Patent Document 1 or 2. Accordingly, in the case where the HCCI engine disclosed in Patent Document 1 or 2 works in the fuel-cut mode appropriately, there rises a possible problem that the combustion of the fuel-air mixture becomes unstable immediately after the working mode is returned from the fuel-cut mode to the normal mode, resulting in a variation on output torque, in other words, the ignited fuel-air mixture gets extinguished immediately after the return to the normal mode, causing a delay in rise of the output torque.